Frederic must have used for_each_possible_cpu() to account for CPUs thatare offline at the time of registration, but may eventually turn online.Since register_wide_hw_breakpoint() interface is designed to deliversystem-wide breakpoints, the debug registers of a new online CPU willshould have the breakpoints populated to comprehensively notify allmemory accesses over target address.

I'd rather wait to hear from Frederic to know whyperf_event_create_kernel_counter() returns an error when run for anoffline cpu and how it can be solved.